Electronic devices such as consumer devices, manufacturing devices, and inspecting devices are specified to undergo an immunity tolerance test (IEC61000-4-2). The immunity test aims to confirm that the electronic device will not malfunction even if it is subjected to electrostatic discharge caused by people touching a portion of the electronic device or aerial discharge. Recently, immunity tolerance of semiconductors has deteriorated since operating margin has been reduced for lower source voltage, and non-metalization of enclosures has been promoted for weight saving of electronic devices. Thus, the environment of the electronic device regarding static electricity is becoming severe from year to year. Countermeasure costs needed to pass the above-mentioned electrostatic test tend to increase as well. Further, malfunctions due to static electricity occur even in the devices that have passed the test, which is now a major problem.
In such situation, a demand for a technology to improve the immunity tolerance and electrostatic resistance characteristics of an electronic device is increasing. It is therefore urgent to develop a component, a PCB or PWB, and an enclosure structure which are adopted to control noise current flowing into a semiconductor (e.g. LSI) that is susceptible to static electricity and to construct designing technology for them. Further, establishing a technology for identifying current paths during the immunity tests or electrostatic tests and elucidating mechanisms where faults occur are important in order to construct the designing technology of the noise suppression component, the PCB or PWB and the enclosure structure.
A current that flows through a screw/spacer portion connecting an enclosure with a PCB or PWB in an electronic device is a key factor for solving immunity issues including static electricity. This is because, particularly in an electrostatic issue, the noise current caused by electrostatic discharge may flow from the enclosure via the screw/spacer to the PCB or PWB, and the noise current that has flown into the PCB or PWB may be released to the enclosure via the screw/spacer.
The current flowing through a screw/spacer portion is also an important factor regarding a problem related to EMI (Electromagnetic Interference) from an electronic device. The noise current generated in a semiconductor such as LSI flows from the PCB or PWB via the screw/spacer portion into the enclosure, thereby causing EMI.
The following technologies are proposed for these issues and problems. “Patent document 1”, “patent document 2” and “patent document 3” describe a screw-like component having a transmission line structure composed of inductance and capacitance to hold low-pass filter characteristics.
In the electronic devices disclosed in “Patent document 4”, “patent document 5”, and “patent document 6”, an enclosure and a PCB or PWB is secured by a metal spacer and the surrounding of the spacer is covered with a magnetic core, thus forming an integrated spacer. “Patent document 4” further describes a technology for inserting a washer-like resistance sheet between a spacer and an enclosure.
On the other hand, in order to identify the cause of EMI from the overall electronic device, “patent document 6” discloses a technology for measuring an electric current flowing through a screw portion connecting the enclosure and PCB or PWB of an electronic device. This relates to a current probe having a coil for detecting magnetic flux caused by the current flowing through the screw portion between the enclosure and PCB or PWB and to a measuring method using the current probe.